1. Field of the Invention
The present invention relates to a fuel cell module in which an electrode member and a separator are integrated, and a manufacturing method thereof.
2. Description of the Related Art
A Fuel cell generating electricity from electrochemical reactions of gases has a high power generation efficiency and an extremely small impact on the environment since the discharged gas is clean. Among these, the proton-exchange membrane fuel cell is capable of operating at relatively low temperatures and has a large output density. For this reason, its application to various fields such as power generation and as a power source for automobiles is anticipated.
In the proton-exchange membrane fuel cell, a cell in which separators sandwich a membrane electrode assembly (MEA) or the like serves as the unit of power generation. The MEA is formed from a polymer membrane (electrolyte membrane) acting as an electrolyte, and a pair of electrode catalyst layers (a fuel electrode (anode) catalyst layer and an oxygen electrode (cathode) catalyst layer) respectively arranged on both sides of the electrolyte membrane in the thickness direction. On the surfaces of the pair of electrode catalyst layers a gas diffusion layer is further disposed. Fuel gas such as hydrogen is supplied to the fuel electrode side, while an oxidizing gas such as oxygen and air is supplied to the oxygen electrode side. The supplied gas, the electrolyte, and the electrode catalyst layers are subjected to an electrochemical reaction at the three-phase boundary to generate electricity. The proton-exchange membrane fuel cell is structured by sandwiching a cell stack in which a plurality of the above cells are stacked together between end plates or the like disposed on both ends of the fuel cell in the cell stacking direction.
A manifold serving as a flow path for gas or water is formed on the peripheral edge portion of the cell stack. Mixing of the gases supplied to the respective electrodes creates issues such as lowered power generation efficiency. Also, the electrolyte membrane exhibits proton conductance in a state with water contained therein. Therefore, during operation the electrolyte must maintain a wet state. Accordingly, in order to prevent gas mixing and leakage, as well as maintain a wet state within the cells, a seal member is disposed on the peripheral edge portion of the manifold and the MEA (see Japanese Patent Application Publication Nos. JP-A-2007-188834, JP-A-2007-149472, and JP-A-2007-66766 for examples).
As disclosed in Japanese Patent Application Publication Nos. JP-A-2007-188834and JP-A-2007-149472, a gasket structure which integrates the electrode member and the seal member is known. In such the gasket structure, liquid rubber is poured into the peripheral edge portion of the electrode member which is formed from the MEA, the gas diffusion layer, and so forth, and injection molding is carried out.
However, such conventional gasket structures are plagued by the following three issues. The first issue is the low mechanical strength of the seal member. In the convention gasket structures, liquid rubber such as silicone rubber is used as the seal member. But most liquid rubber has a low molecular weight. As a consequence, there is little tensile strength after crosslinking. Since the liquid rubber also does not stretch much, the liquid rubber does not easily follow the expansion and contraction of the electrolyte membrane as a result of moisture and the like. Furthermore, silicone rubber does not have sufficient adhesiveness or acid resistance, which is problematic in terms of sealability and durability.
The second issue concerns the need for special treatment when liquid rubber is used so that the liquid rubber does not excessively impregnate a porous layer during molding. Namely, when pouring and molding liquid rubber into the peripheral edge portion of the electrode member, the liquid rubber impregnates porous layers such as the gas diffusion layer. In such case, impregnation of the liquid rubber is difficult to control. Therefore, the flow of gas is impeded at regions excessively impregnated with the liquid rubber, and power generation performance is reduced by a corresponding amount. To regulate the amount of liquid rubber impregnated, in Japanese Patent Application Publication No. JP-A-2007-188834 for example, the porosity of a part of the porous layer is decreased in advance by plugging or the like. Also, in Japanese Patent Application Publication No. JP-A-2007-149472, a part of the porous layer is compressed to increase density.
The third issue is the risk of deformation of the electrolyte membrane during injection molding due to the injection pressure of the liquid rubber. The electrolyte membrane is a thin polymer film. Therefore, the flow of liquid rubber during injection molding may press against and deform the electrolyte membrane. If the electrolyte membrane is deformed, obtaining a desired power generation performance becomes difficult.
As mentioned above, the proton-exchange membrane fuel cell is structured by stacking a plurality of electrode members, in which the MEA, the gas diffusion layer, and the like are stacked, via separators. In addition to the positioning of each member, the stacking operation performed while maintaining each of the members at predetermined positions is difficult. For this reason, the assembly operation is extremely laborious and results in poor productivity. As examples, according to the gasket structures disclosed in Japanese Patent Application Publication Nos. JP-A-2007-188834, JP-A-2007-149472, and JP-A-2007-66766, the electrode member is integrated, which facilitates stacking by a corresponding amount. However, since the gasket structure and the separators are separate, the above issue is not resolved due to the difficulty of positioning and so forth. Accordingly, the assembly operation must be made more efficient. Inspections are also sometimes required to determine whether there are defects in any of the cells. However, it is difficult at present to take apart an assembled proton-exchange membrane fuel cell for inspection and repair.